Apparatus having integrated circuit well structures of vertical and/or retrograde profiles

ABSTRACT

Transistors having a control gate isolated from a first region of semiconductor material having a first conductivity type, first and second source/drain regions having a second conductivity type different than the first conductivity type and formed in the first region of semiconductor material, and a second region of semiconductor material having the first conductivity type in contact with the first region of semiconductor material, wherein the first region of semiconductor material is between the control gate and the second region of semiconductor material, wherein the first region of semiconductor material has a first width, and wherein the second region of semiconductor material has a second width, less than or equal to the first width, as well as memory containing such transistors.

RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No. 15/892,584 filed on Feb. 9, 2018 and titled “METHODS OF FORMING INTEGRATED CIRCUIT WELL STRUCTURES,” (allowed), which claims the benefit of U.S. Provisional Patent Application Ser. No. 62/611,694, filed Dec. 29, 2017 and titled, “METHODS OF FORMING INTEGRATED CIRCUIT WELL STRUCTURES,” which is commonly assigned and incorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure relates generally to integrated circuits and, in particular, in one or more embodiments, the present disclosure relates to methods of forming integrated circuit well structures and memory containing such well structures.

BACKGROUND

Integrated circuit devices traverse a broad range of electronic devices. One particular type include memory devices, oftentimes referred to simply as memory. Memory devices are typically provided as internal, semiconductor, integrated circuit devices in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.

Flash memory has developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage (Vt) of the memory cells, through programming (which is often referred to as writing) of charge storage structures (e.g., floating gates or charge traps) or other physical phenomena (e.g., phase change or polarization), determine the data state (e.g., data value) of each memory cell. Common uses for flash memory and other non-volatile memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, mobile telephones, and removable memory modules, and the uses for non-volatile memory continue to expand.

A NAND flash memory is a common type of flash memory device, so called for the logical form in which the basic memory cell configuration is arranged. Typically, the array of memory cells for NAND flash memory is arranged such that the control gate of each memory cell of a row of the array is connected together to form an access line, such as a word line. Columns of the array include strings (often termed NAND strings) of memory cells connected together in series between a pair of select gates, e.g., a source select transistor and a drain select transistor. Each source select transistor may be connected to a source, while each drain select transistor may be connected to a data line, such as column bit line. Variations using more than one select gate between a string of memory cells and the source, and/or between the string of memory cells and the data line, are known.

In order for memory manufacturers to remain competitive, memory designers are constantly striving to increase the density of memory devices. Increasing the density of a memory device often involves reducing spacing between circuit elements. However, reduced spacing of circuit elements may hinder effective isolation of adjacent circuit elements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a memory in communication with a processor as part of an electronic system, according to an embodiment.

FIGS. 2A-2B are schematics of portions of an array of memory cells as could be used in a memory of the type described with reference to FIG. 1.

FIG. 3 depicts a related integrated circuit structure.

FIGS. 4A-4H depict an integrated circuit structure during various stages of fabrication in accordance with embodiments.

FIG. 5A is a schematic of a portion of an array of memory cells as could be used in a memory device of the type described with reference to FIG. 1.

FIG. 5B is a cross-sectional view of a block select transistor of FIG. 4A formed on a portion of the integrated circuit structure of FIG. 3F-3H.

FIG. 6 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with an embodiment.

FIG. 7 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with an embodiment.

FIG. 8 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with an embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown, by way of illustration, specific embodiments. In the drawings, like reference numerals describe substantially similar components throughout the several views. Other embodiments may be utilized and structural, logical and electrical changes may be made without departing from the scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense.

The term “semiconductor” used herein can refer to, for example, a layer of material, a wafer, or a substrate, and includes any base semiconductor structure. “Semiconductor” is to be understood as including silicon-on-sapphire (SOS) technology, silicon-on-insulator (SOI) technology, thin film transistor (TFT) technology, doped and undoped semiconductors, epitaxial layers of a silicon supported by a base semiconductor structure, as well as other semiconductor structures well known to one skilled in the art. Furthermore, when reference is made to a semiconductor in the following description, previous process steps may have been utilized to form regions/junctions in the base semiconductor structure, and the term semiconductor can include the underlying layers containing such regions/junctions.

The term “conductive” as used herein, as well as its various related forms, e.g., conduct, conductively, conducting, conduction, conductivity, etc., refers to electrically conductive unless otherwise apparent from the context. Similarly, the term “connecting” as used herein, as well as its various related forms, e.g., connect, connected, connection, etc., refers to electrically connecting unless otherwise apparent from the context.

FIG. 1 is a simplified block diagram of a first apparatus (e.g., an integrated circuit device), in the form of a memory (e.g., memory device) 100, in communication with a second apparatus, in the form of a processor 130, as part of a third apparatus, in the form of an electronic system, according to an embodiment. Some examples of electronic systems include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones and the like. The processor 130, e.g., a controller external to the memory device 100, may be a memory controller or other external host device.

Memory device 100 includes an array of memory cells 104 logically arranged in rows and columns. Memory cells of a logical row are typically connected to the same access line (commonly referred to as a word line) while memory cells of a logical column are typically selectively connected to the same data line (commonly referred to as a bit line). A single access line may be associated with more than one logical row of memory cells and a single data line may be associated with more than one logical column. Memory cells (not shown in FIG. 1) of at least a portion of array of memory cells 104 are capable of being programmed to one of at least two data states.

A row decode circuitry 108 and a column decode circuitry 110 are provided to decode address signals. Address signals are received and decoded to access the array of memory cells 104. Memory device 100 also includes input/output (I/O) control circuitry 112 to manage input of commands, addresses and data to the memory device 100 as well as output of data and status information from the memory device 100. An address register 114 is in communication with I/O control circuitry 112 and row decode circuitry 108 and column decode circuitry 110 to latch the address signals prior to decoding. A command register 124 is in communication with I/O control circuitry 112 and control logic 116 to latch incoming commands.

A controller (e.g., the control logic 116 internal to the memory device 100) controls access to the array of memory cells 104 in response to the commands and generates status information for the external processor 130, i.e., control logic 116 is configured to perform access operations (e.g., read operations, program operations and/or erase operations) and other operations in accordance with embodiments described herein. The control logic 116 is in communication with row decode circuitry 108 and column decode circuitry 110 to control the row decode circuitry 108 and column decode circuitry 110 in response to the addresses.

Control logic 116 may also be in communication with a cache register 118. Cache register 118 may latch data, either incoming or outgoing, as directed by control logic 116 to temporarily store data while the array of memory cells 104 is busy writing or reading, respectively, other data. During a program operation (e.g., write operation), data may be passed from the cache register 118 to data register 120 for transfer to the array of memory cells 104; then new data may be latched in the cache register 118 from the I/O control circuitry 112. During a read operation, data may be passed from the cache register 118 to the I/O control circuitry 112 for output to the external processor 130; then new data may be passed from the data register 120 to the cache register 118. A status register 122 is in communication with I/O control circuitry 112 and control logic 116 to latch the status information for output to the processor 130.

Memory device 100 receives control signals at control logic 116 from processor 130 over a control link 132. The control signals might include a chip enable CE #, a command latch enable CLE, an address latch enable ALE, a write enable WE #, a read enable RE #, and a write protect WP #. Additional or alternative control signals (not shown) may be further received over control link 132 depending upon the nature of the memory device 100. Memory device 100 receives command signals (which represent commands), address signals (which represent addresses), and data signals (which represent data) from processor 130 over a multiplexed input/output (I/O) bus 134 and outputs data to processor 130 over I/O bus 134.

For example, the commands may be received over input/output (I/O) pins [7:0] of I/O bus 134 at I/O control circuitry 112 and may be written into command register 124. The addresses may be received over input/output (I/O) pins [7:0] of I/O bus 134 at I/O control circuitry 112 and may be written into address register 114. The data may be received over input/output (I/O) pins [7:0] for an 8-bit device or input/output (I/O) pins [15:0] for a 16-bit device at I/O control circuitry 112 and may be written into cache register 118. The data may be subsequently written into data register 120 for programming the array of memory cells 104. For another embodiment, cache register 118 may be omitted, and the data may be written directly into data register 120. Data may also be output over input/output (I/O) pins [7:0] for an 8-bit device or input/output (I/O) pins [15:0] for a 16-bit device. The I/O bus 134 might further include complementary data strobes DQS and DQSN that may provide a synchronous reference for data input and output. Although reference may be made to I/O pins, they may include any conductive node providing for electrical connection to the memory device 100 by an external device (e.g., processor 130), such as conductive pads or conductive bumps as are commonly used.

It will be appreciated by those skilled in the art that additional circuitry and signals can be provided, and that the memory device 100 of FIG. 1 has been simplified. It should be recognized that the functionality of the various block components described with reference to FIG. 1 may not necessarily be segregated to distinct components or component portions of an integrated circuit device. For example, a single component or component portion of an integrated circuit device could be adapted to perform the functionality of more than one block component of FIG. 1. Alternatively, one or more components or component portions of an integrated circuit device could be combined to perform the functionality of a single block component of FIG. 1.

Additionally, while specific I/O pins are described in accordance with popular conventions for receipt and output of the various signals, it is noted that other combinations or numbers of I/O pins may be used in the various embodiments.

FIG. 2A is a schematic of a portion of an array of memory cells 200A as could be used in a memory of the type described with reference to FIG. 1, e.g., as a portion of array of memory cells 104. Memory array 200A includes access lines, such as word lines 202 ₀ to 202 _(N), and data lines, such as bit lines 204 ₀ to 204 _(M). The word lines 202 may be connected to global access lines (e.g., global word lines), not shown in FIG. 2A, in a many-to-one relationship. For some embodiments, memory array 200A may be formed over a semiconductor that, for example, may be conductively doped to have a conductivity type, such as a p-type conductivity, e.g., to form a p-well, or an n-type conductivity, e.g., to form an n-well.

Memory array 200A might be arranged in rows (each corresponding to a word line 202) and columns (each corresponding to a bit line 204). Each column may include a string of series-connected memory cells (e.g., non-volatile memory cells), such as one of NAND strings 206 ₀ to 206 _(M). Each NAND string 206 might be connected (e.g., selectively connected) to a common source (SRC) 216 and might include memory cells 208 ₀ to 208 _(N). The memory cells 208 may represent non-volatile memory cells for storage of data. The memory cells 208 of each NAND string 206 might be connected in series between a select gate 210 (e.g., a field-effect transistor), such as one of the select gates 210 ₀ to 210 _(M) (e.g., that may be source select transistors, commonly referred to as select gate source), and a select gate 212 (e.g., a field-effect transistor), such as one of the select gates 212 ₀ to 212 _(M) (e.g., that may be drain select transistors, commonly referred to as select gate drain). Select gates 210 ₀ to 210 _(M) might be commonly connected to a select line 214, such as a source select line (SGS), and select gates 212 ₀ to 212 _(M) might be commonly connected to a select line 215, such as a drain select line (SGD). Although depicted as traditional field-effect transistors, the select gates 210 and 212 may utilize a structure similar to (e.g., the same as) the memory cells 208. The select gates 210 and 212 might represent a plurality of select gates connected in series, with each select gate in series configured to receive a same or independent control signal.

A source of each select gate 210 might be connected to common source 216. The drain of each select gate 210 might be connected to a memory cell 208 ₀ of the corresponding NAND string 206. For example, the drain of select gate 210 ₀ might be connected to memory cell 208 ₀ of the corresponding NAND string 206 ₀. Therefore, each select gate 210 might be configured to selectively connect a corresponding NAND string 206 to common source 216. A control gate of each select gate 210 might be connected to select line 214.

The drain of each select gate 212 might be connected to the bit line 204 for the corresponding NAND string 206. For example, the drain of select gate 212 ₀ might be connected to the bit line 204 ₀ for the corresponding NAND string 206 ₀. The source of each select gate 212 might be connected to a memory cell 208 _(N) of the corresponding NAND string 206. For example, the source of select gate 212 ₀ might be connected to memory cell 208 _(N) of the corresponding NAND string 206 ₀. Therefore, each select gate 212 might be configured to selectively connect a corresponding NAND string 206 to the corresponding bit line 204. A control gate of each select gate 212 might be connected to select line 215.

The memory array in FIG. 2A might be a three-dimensional memory array, e.g., where NAND strings 206 may extend substantially perpendicular to a plane containing the common source 216 and to a plane containing a plurality of bit lines 204 that may be substantially parallel to the plane containing the common source 216.

Typical construction of memory cells 208 includes a data-storage structure 234 (e.g., a floating gate, charge trap, etc.) that can determine a data state of the memory cell (e.g., through changes in threshold voltage), and a control gate 236, as shown in FIG. 2A. The data-storage structure 234 may include both conductive and dielectric structures while the control gate 236 is generally formed of one or more conductive materials. In some cases, memory cells 208 may further have a defined source/drain (e.g., source) 230 and a defined source/drain (e.g., drain) 232. Memory cells 208 have their control gates 236 connected to (and in some cases form) a word line 202.

A column of the memory cells 208 may be a NAND string 206 or a plurality of NAND strings 206 selectively connected to a given bit line 204. A row of the memory cells 208 may be memory cells 208 commonly connected to a given word line 202. A row of memory cells 208 can, but need not, include all memory cells 208 commonly connected to a given word line 202. Rows of memory cells 208 may often be divided into one or more groups of physical pages of memory cells 208, and physical pages of memory cells 208 often include every other memory cell 208 commonly connected to a given word line 202. For example, memory cells 208 commonly connected to word line 202 _(N) and selectively connected to even bit lines 204 (e.g., bit lines 204 ₀, 204 ₂, 204 ₄, etc.) may be one physical page of memory cells 208 (e.g., even memory cells) while memory cells 208 commonly connected to word line 202 _(N) and selectively connected to odd bit lines 204 (e.g., bit lines 204 ₁, 204 ₃, 204 ₅, etc.) may be another physical page of memory cells 208 (e.g., odd memory cells). Although bit lines 204 ₃-204 ₅ are not explicitly depicted in FIG. 2A, it is apparent from the figure that the bit lines 204 of the array of memory cells 200A may be numbered consecutively from bit line 204 ₀ to bit line 204 _(M). Other groupings of memory cells 208 commonly connected to a given word line 202 may also define a physical page of memory cells 208. For certain memory devices, all memory cells commonly connected to a given word line might be deemed a physical page of memory cells. The portion of a physical page of memory cells (which, in some embodiments, could still be the entire row) that is read during a single read operation or programmed during a single programming operation (e.g., an upper or lower page of memory cells) might be deemed a logical page of memory cells. A block of memory cells may include those memory cells that are configured to be erased together, such as all memory cells connected to word lines 202 ₀-202 _(N) (e.g., all NAND strings 206 sharing common word lines 202). Unless expressly distinguished, a reference to a page of memory cells herein refers to the memory cells of a logical page of memory cells.

FIG. 2B is another schematic of a portion of an array of memory cells 200B as could be used in a memory of the type described with reference to FIG. 1, e.g., as a portion of array of memory cells 104. Like numbered elements in FIG. 2B correspond to the description as provided with respect to FIG. 2A. FIG. 2B provides additional detail of one example of a three-dimensional NAND memory array structure. The three-dimensional NAND memory array 200B may incorporate vertical structures which may include semiconductor pillars where a portion of a pillar may act as a channel region of the memory cells of NAND strings 206. The NAND strings 206 may be each selectively connected to a bit line 204 ₀-204 _(M) by a select transistor 212 (e.g., that may be drain select transistors, commonly referred to as select gate drain) and to a common source 216 by a select transistor 210 (e.g., that may be source select transistors, commonly referred to as select gate source). Multiple NAND strings 206 might be selectively connected to the same bit line 204. Subsets of NAND strings 206 can be connected to their respective bit lines 204 by biasing the select lines 215 ₀-215 _(K) to selectively activate particular select transistors 212 each between a NAND string 206 and a bit line 204. The select transistors 210 can be activated by biasing the select line 214. Each word line 202 may be connected to multiple rows of memory cells of the memory array 200B. Rows of memory cells that are commonly connected to each other by a particular word line 202 may collectively be referred to as tiers.

Various circuit elements may be formed on well structures of varying types and levels of conductivity. FIG. 3 depicts a related integrated circuit structure demonstrating two adjacent well structures and their limitations. In general, a well structure might be formed of one or more regions (e.g., doped regions) of semiconductor material 346 in a semiconductor material 340. One of the regions of semiconductor material 346 (e.g., 346₀) is typically formed over, and often in contact with, a region of semiconductor material 338. The region of semiconductor material 338 might have a conductivity type, such as an n-type conductivity. The regions of semiconductor material 346 (e.g., each region of semiconductor material 346 ₀-346 ₂) might have a conductivity type the same as the conductivity type of the region of semiconductor material 338, such as an n-type conductivity. The semiconductor material 340 might have a conductivity type that is different than (e.g., opposite of) the conductivity type of the semiconductor material 338, such as a p-type conductivity. In combination, the regions of semiconductor material 346 ₀-346 ₂ and the region of semiconductor material 338 form a contiguous structure often referred to as a tub. The enclosed portion of the semiconductor material 340 between two stacks of the regions of semiconductor material 346 ₀-346 ₂ in contact with the region of semiconductor material 338, e.g., within the tub, may represent a well having a different conductivity type than the well structures of the regions of semiconductor material 346.

Each of the regions of semiconductor material 346 might be formed by implanting a dopant species into the semiconductor material 340. As is well understood in the art, such implantation generally involves acceleration of ions directed at a surface of the semiconductor material 340. To produce an n-type conductivity, the dopant species might include ions of arsenic (As), antimony (Sb), phosphorus (P) or another n-type impurity. To produce a p-type conductivity, the dopant species might include ions of boron (B) or another p-type impurity.

Each of the regions of semiconductor material 346 might be formed at different implant energy levels. Higher implant energy levels may generally lead to deeper doped regions for a given dopant species. For example, the region of semiconductor material 346 ₀ might be formed at a first implant energy level, the region of semiconductor material 346 ₁ might be formed at a second implant energy level less than the first implant energy level, and the region of semiconductor material 346 ₂ might be formed at a third implant energy level less than the second implant energy level. The region of semiconductor material 338 might be similarly formed, e.g., by implanting a dopant species into the semiconductor material 340, e.g., at a higher implant energy level than is used for any of the regions of semiconductor material 346 ₀-346 ₂.

While higher energy implants generally form doped regions at deeper levels (e.g., farther from the surface of the semiconductor material 340) for a given dopant species, they may also lead to an increased level of dopant migration or straggle, such that the region 346 ₀ might be wider than the region 346 ₁ which might be wider than the region 346 ₂. As the spacing between adjacent well structures narrows, isolation characteristics might diminish and might lead to punch-through, or breakdown, between the adjacent well structures. Various embodiments may mitigate such widening of the doped regions of a multi-level well structure. Various embodiments may seek to form well structures having vertical or retrograde profiles.

FIGS. 4A-4H depict an integrated circuit structure during various stages of fabrication in accordance with embodiments. FIG. 4A depicts a semiconductor material 440 over a region of semiconductor material 438. The semiconductor materials 438 and 440 may each comprise silicon, such as monocrystalline silicon, or other semiconductor material. The semiconductor material 440 might have a conductivity type that is different than (e.g., opposite of) the conductivity type of the semiconductor material 438. For example, the semiconductor material 438 might have a first conductivity type (e.g., an n-type conductivity) and the semiconductor material 440 might have second conductivity type (e.g., a p-type conductivity). The region of semiconductor material 438 might be formed by implanting a dopant species (e.g., one or more dopant species) into the semiconductor material 440. Alternatively, the semiconductor material 440 might be formed over and subsequent to forming the semiconductor material 438, such as by epitaxial growth, chemical vapor deposition, physical vapor deposition, etc.

A patterned mask 442 ₀ might be formed over the semiconductor material 440. The patterned mask 442 ₀ might have an opening 454 ₀ exposing a portion of the semiconductor material 440 and having a width 448 ₀. The patterned mask 442 ₀ might further have a thickness 450 ₀. As one example, the thickness 450 ₀ might be 3-4 μm, e.g., 3.3 μm. The patterned mask 442 ₀ might represent a patterned photoresist material, or any other material configured to impede (e.g., block) implantation of dopant species.

Photolithographic processes are often used to define a desired pattern in integrated circuit fabrication. In a photolithographic process, a photoresist layer may be formed on the surface of the in-process device. The photoresist layer may contain a photo-sensitive polymer whose ease of removal is altered upon exposure to light or other electromagnetic radiation. To define the pattern, the photoresist layer may be selectively exposed to radiation and then developed to expose portions of the underlying layer. In a positive resist system, the portions of the photoresist layer exposed to the radiation are photosolubilized and a photolithographic mask is designed to block the radiation from those portions of the photoresist layer that are to remain after developing. In a negative resist systems, the portions of the photoresist layer exposed to the radiation are photopolymerized and the photolithographic mask is designed to block the radiation from those portions of the photoresist layer that are to be removed by developing.

In FIG. 4B, a dopant species might be accelerated (e.g., implanted) into the semiconductor material 440 through the opening 454 ₀. For example, a beam of ions 444 ₀ might be directed at the surface of the semiconductor material 440 to form a region of semiconductor material 446 ₀, which might be in contact with the region of semiconductor material 438. The region of semiconductor material 446 ₀ might have the first conductivity type. Although the region of semiconductor material 446 ₀ is depicted as having a rectangular profile, those of ordinary skill in the art will recognize that the profile shape may generally be more amorphous in nature. The region of semiconductor material 446 ₀ might be formed at a first level within the semiconductor material 440 nominally extending (e.g., extending) from a first depth 452 ₀ from the surface of the semiconductor material 440 (e.g., in contact with the region of semiconductor material 438) to a second depth 452 ₁ (e.g., to at least the second depth 452 ₁) from the surface of the semiconductor material 440.

In FIG. 4C, the patterned mask 442 ₀ of FIGS. 4A-4B is subjected to an isotropic removal process, such as an isotropic wet etch, an isotropic dry plasma etch, a dry-strip plasma clean, etc., to form the patterned mask 442 ₁. The patterned mask 442 ₁ might have an opening 454 ₁ exposing a portion of the semiconductor material 440 and having a width 448 ₁. The patterned mask 442 ₁ might further have a thickness 450 ₁. Isotropic removal processes generally remove materials (e.g., uniformly) in all directions of contact, e.g., reducing thicknesses and widening openings of surface materials being removed. Accordingly, the width 448 ₁ may be greater (e.g., wider) than the width 448 ₀, while the thickness 450 ₁ may be less (e.g., narrower) than the thickness 450 ₀. As one example, the thickness 450 ₁ might be 1.5-2.5 μm, e.g., 2 μm.

In FIG. 4D, a dopant species might be accelerated (e.g., implanted) into the semiconductor material 440 through the opening 454 ₁. For example, a beam of ions 444 ₁ might be directed at the surface of the semiconductor material 440 to form a region of semiconductor material 446 ₁, which might be in contact with the region of semiconductor material 446 ₀. The region of semiconductor material 446 ₁ might have the first conductivity type. Although the region of semiconductor material 446 ₁ is depicted as having a rectangular profile, those of ordinary skill in the art will recognize that the profile shape may generally be more amorphous in nature. The region of semiconductor material 446 ₁ might be formed at a second level within the semiconductor material 440 nominally extending (e.g., extending) from the second depth 452 ₁ (e.g., from at least the second depth 452 ₁) to a third depth 452 ₂ (e.g., to at least the third depth 452 ₂) from the surface of the semiconductor material 440.

The dopant species used to form the region of semiconductor material 446 ₁ may be the same as, or different than, the dopant species used to form the region of semiconductor material 446 ₀, while having a same conductivity type. For example, the dopant species used to form the region of semiconductor material 446 ₀ and the region of semiconductor material 446 ₁ might both be phosphorus to form regions of n-type conductivity. Alternatively, the dopant species used to form the region of semiconductor material 446 ₀ might be phosphorus to form a region of n-type conductivity, while the dopant species used to form the region of semiconductor material 446 ₁ might be arsenic to also form a region of n-type conductivity.

In FIG. 4E, the patterned mask 442 ₁ of FIGS. 4C-4D is subjected to an isotropic removal process, such as an isotropic wet etch, an isotropic dry plasma etch, a dry-strip plasma clean, etc., to form the patterned mask 442 ₂. The patterned mask 442 ₂ might have an opening 454 ₂ exposing a portion of the semiconductor material 440 and having a width 448 ₂. The patterned mask 442 ₂ might further have a thickness 450 ₂. The width 448 ₂ may be greater (e.g., wider) than the width 448 ₁, while the thickness 450 ₂ may be less (e.g., narrower) than the thickness 450 ₁. As one example, the thickness 450 ₂ might be 0.5-1.0 μm, e.g., 0.8 μm.

In FIG. 4F, a dopant species might be accelerated (e.g., implanted) into the semiconductor material 440 through the opening 454 ₂. For example, a beam of ions 444 ₂ might be directed at the surface of the semiconductor material 440 to form a region of semiconductor material 446 ₂, which might be in contact with the region of semiconductor material 446 ₁. The region of semiconductor material 446 ₂ might have the first conductivity type. Although the region of semiconductor material 446 ₂ is depicted as having a rectangular profile, those of ordinary skill in the art will recognize that the profile shape may generally be more amorphous in nature. The region of semiconductor material 446 ₂ might be formed at a third level within the semiconductor material 440 nominally extending (e.g., extending) from the third depth 452 ₂ (e.g., from at least the third depth 452 ₂) to a fourth depth 452 ₃ from the surface of the semiconductor material 440, which may be coincident with the surface of the semiconductor material 440. The dopant species used to form the region of semiconductor material 446 ₂ may be the same as, or different than, the dopant species used to form the region of semiconductor material 446 ₁, while having a same conductivity type.

While FIGS. 4A-4F depicted a well structure of a single stack of regions of semiconductor material 446, such well structures would typically be used to form tubs, e.g., enclosing a portion of the semiconductor material 440 (e.g., a well) having the second conductivity type within a tub of material having the first conductivity type. FIGS. 4G and 4H each depict a well 456 in a portion of the semiconductor material 440 that is isolated from adjacent portions of the semiconductor material 440 by regions of semiconductor material 438 and 446 having the first conductivity type. By utilizing the isotropic removal of the patterned mask between the formation of regions of semiconductor material 446 at adjacent levels, a generally vertical profile of the regions of semiconductor material 446 might be generated, such as depicted in FIG. 4G, with widths of each resulting region of semiconductor material being similar (e.g., the same). Additionally, as the risk of punch-through might be more severe at lower levels of the regions of semiconductor material 446, a retrograde profile of the regions of semiconductor material 446 might be generated, such as depicted in FIG. 4H, in order to increase the spacing between adjacent regions of semiconductor material 446 at the lower levels, e.g., by reducing the resulting widths of regions of semiconductor material 446 at lower levels, without affecting the spacing between adjacent regions of semiconductor material near (e.g., at) the surface of the semiconductor material 440. While each region of semiconductor material 446 formed at one level (e.g., for a corresponding range of depths from the surface of the semiconductor material 440) is depicted in FIG. 4H to be wider than each region of semiconductor material 446 formed at a lower level (e.g., for a different corresponding range of depths farther from the surface of the semiconductor material 440), other options might be used. For example, the regions of semiconductor material 446 ₁ and 446 ₂ might have similar widths, such as shown and described with reference to FIG. 4G, and the region of semiconductor material 446 ₀ might have a width less than the width of the region of semiconductor material 446 ₁, such as shown and described with reference to FIG. 4H.

By characterizing the implantation of desired dopant species at different levels of the semiconductor material 440, as might be determined experimentally, empirically or through simulation, desired widths of openings 454 could be determined for each desired level to produce the desired profile. Similarly, by characterizing the isotropic removal of the patterned mask 442, as might be determined experimentally, empirically or through simulation, a desired initial thickness could be determined that would permit formation of each of the subsequent desired widths of the openings 454 while maintaining sufficient thickness to impede implantation of dopant species where such is not desired. While three levels of regions of semiconductor material 446 were shown and described with reference to FIGS. 4A-4H, fewer or more levels of regions of semiconductor material 446 might be used in accordance with embodiments.

Different types of circuitry might be formed over the regions of semiconductor material 446 (e.g., regions of semiconductor material 446 ₂) versus the well 456. For example, p-type field-effect transistors (pFETs) might be formed in adjacent semiconductor regions 446 ₂ (e.g., as part of circuitry to select different blocks of memory cells of an array of memory cells for access), while n-type field-effect transistors (nFETs) might be formed in the well 456. FIGS. 5A-5B provide an example of the use of a region of semiconductor material 446 in a memory.

As referenced with respect to FIG. 2A, local access lines, e.g., word lines 202, may be connected to global access lines in a many-to-one relationship. FIG. 5A is a schematic of a portion of an array of memory cells as could be used in a memory device of the type described with reference to FIG. 1 and depicting this many-to-one relationship between local access lines (e.g., word lines 202) and global access lines (e.g., global word lines 502).

As depicted in FIG. 5A, a plurality of blocks of memory cells 562 may have their local access lines (e.g., word lines 202) commonly selectively connected to a plurality of global access lines (e.g., global word lines 502). A block of memory cells 562 may include a plurality of NAND strings 206 commonly coupled to a particular set of word lines 202. For example, the NAND strings 206 ₀-206 _(M) of FIG. 2A, or some portion thereof, may represent a block of memory cells 562. Although FIG. 5A depicts only blocks of memory cells 562 ₀ and 562 ₁ (Block 0 and Block 1), additional blocks of memory cells 562 may have their word lines 202 commonly connected to global word lines 502 in a like manner. Similarly, although FIG. 5A depicts only four word lines 202, blocks of memory cells 562 may include fewer or more word lines 202. In applying the structure of FIG. 5A to the array structures of FIGS. 2A-2B, it is clear that there would be N+1 global word lines 502, i.e., GWL 502 ₀ to 502 _(N).

To facilitate memory access operations to specific blocks of memory cells 562 commonly coupled to a given set of global word lines 502, each block of memory cells 562 may have a corresponding set of block select transistors 558 in a one-to-one relationship with their word lines 202. Control gates of the set of block select transistors 558 for a given block of memory cells 562 may have their control gates commonly connected to a corresponding block select line 560. For example, for block of memory cells 562 ₀, word line 202 ₀₀ may be selectively connected to global word line 502 ₀ through block select transistor 558 ₀₀, word line 202 ₀₁ may be selectively connected to global word line 502 ₁ through block select transistor 558 ₀₁, word line 202 ₀₂ may be selectively connected to global word line 502 ₂ through block select transistor 558 ₀₂, and word line 202 ₀₃ may be selectively connected to global word line 502 ₃ through block select transistor 558 ₀₃, while block select transistors 558 ₀₀-554 ₀₃ are responsive to a control signal (e.g., a common control signal) received on block select line 560 ₀.

Block select transistors may be high-voltage devices. Such switching devices may require increased isolation. FIG. 5B is a cross-sectional view of a block select transistor 558, having a control gate 566 and source/drain regions 564, wherein the control gate 566 is connected to a block select line 560. The block select transistor 558 may be formed in a region of semiconductor material 446 (e.g., a region of semiconductor material 446 ₂ of FIG. 4F), e.g., after removal of the patterned mask 442. For a high-voltage pFET, the regions of semiconductor material 446 might have an N-level of conductivity to provide a high breakdown voltage, e.g., greater than about 30V.

FIG. 6 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with an embodiment. At 671, a patterned mask might be formed having an opening and exposing a semiconductor material (e.g., a portion of a surface of the semiconductor material). For example, a patterned mask might be formed over (e.g., on) a surface of the semiconductor material. At 673, a first doped region might be formed at a first level of the semiconductor level through the opening. At 675, a portion of the patterned mask might be removed isotropically to increase a width of the opening. And at 677, a second doped region might then be formed at a second level of the semiconductor level through the opening.

For some embodiments, additional doped regions might be formed at additional levels of the semiconductor material. Accordingly, the process might proceed to 679, where an additional portion (e.g., second portion) of the patterned mask might be removed isotropically to increase (e.g., further increase) the width of the opening. Subsequently, at 681, an additional doped region (e.g., third doped region) might be formed at an additional level (e.g., third level) of the semiconductor level through the opening. This processing might be repeated for one or more additional doped regions of semiconductor material.

FIG. 7 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with an embodiment. At 781, a patterned mask might be formed having an opening and exposing a semiconductor material (e.g., a portion of a surface of the semiconductor material). For example, a patterned mask might be formed over (e.g., on) a surface of the semiconductor material. At 783, a first dopant species might be implanted in the semiconductor material through the opening and using a first implant energy level. For example, the first dopant species might be phosphorus and the first implant energy level might be approximately 100 KeV, e.g., 960 KeV.

At 785, the patterned mask might be isotropically etched to increase a width of the opening. And at 787, a second dopant species might be implanted in the semiconductor material through the opening and using a second implant energy level less than the first implant energy level. The second dopant species might be the same as, or different from, the first dopant species. The second dopant species might provide a same conductivity type as the first dopant species. For example, the second dopant species might be phosphorus and the second implant energy level might be approximately 300-400 KeV, e.g., 320 KeV.

For some embodiments, additional doped species might be implanted at different implant energy levels. Accordingly, the process might proceed to 789, where the patterned mask might again be isotropically etched to increase (e.g., further increase) the width of the opening. At 791, an additional dopant species might be implanted in the semiconductor material through the opening and using an additional (e.g., second) implant energy level less than a prior (e.g., the first) implant energy level. The additional dopant species might be the same as, or different from, the prior (e.g., second) dopant species. The additional dopant species might provide a same conductivity type as the prior dopant species. For example, the additional dopant species might be phosphorus and the additional implant energy level might be approximately 100-200 KeV, e.g., 150 KeV. This processing might be repeated for one or more additional doped regions of semiconductor material. The implant energy level selected for implanting a dopant species at the surface of the semiconductor material might be chosen in response to desired electrical properties of circuitry formed in that region of semiconductor material.

For some embodiments, dopant species might be implanted through an opening of a particular width at more than one implant energy level, e.g., to increase a range of depth of a resulting doped region of semiconductor material. FIG. 8 is a flowchart of a method of forming a portion of an integrated circuit device in accordance with such an embodiment, as an extension of the method of FIG. 7. For example, proceeding from 787 of FIG. 7, at third dopant species might be implanted in the semiconductor material through the opening and using a third implant energy level less than the second implant energy level. The third dopant species might be the same as, or different from, the second dopant species. The third dopant species might provide a same conductivity type as the second dopant species. For example, the third dopant species might be phosphorus and the second implant energy level might be approximately 100-200 KeV, e.g., 150 KeV. One or more additional dopant species might be implanted at successively lesser energy implant energy levels prior to isotropically etching the patterned mask. The process might then optionally proceed to 789 of FIG. 7.

CONCLUSION

Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement that is calculated to achieve the same purpose may be substituted for the specific embodiments shown. Many adaptations of the embodiments will be apparent to those of ordinary skill in the art. Accordingly, this application is intended to cover any adaptations or variations of the embodiments. 

What is claimed is:
 1. A transistor, comprising: a control gate isolated from a first region of semiconductor material having a first conductivity type; a first source/drain region having a second conductivity type different than the first conductivity type and formed in the first region of semiconductor material; a second source/drain region having the second conductivity type and formed in the first region of semiconductor material; and a second region of semiconductor material having the first conductivity type in contact with the first region of semiconductor material, wherein the first region of semiconductor material is between the control gate and the second region of semiconductor material; wherein the first region of semiconductor material has a first width extending in a first direction from the first source/drain region to the second source/drain region; and wherein the second region of semiconductor material has a second width, less than or equal to the first width, extending in the first direction.
 2. The transistor of claim 1, wherein the second conductivity type is opposite the first conductivity type.
 3. The transistor of claim 2, wherein the first conductivity type is an n-type conductivity and wherein the second conductivity type is a p-type conductivity.
 4. The transistor of claim 1, wherein the second width is less than the first width.
 5. The transistor of claim 1, wherein the first region of semiconductor material comprises a first dopant species, and wherein the second region of semiconductor material comprises a second dopant species.
 6. The transistor of claim 5, wherein the first dopant species and the second dopant species are a same dopant species.
 7. The transistor of claim 5, wherein the first dopant species and the second dopant species each comprise an element selected from a group consisting of arsenic, antimony, phosphorus and boron.
 8. The transistor of claim 1, further comprising: a third region of semiconductor material having the first conductivity type in contact with the second region of semiconductor material, wherein the second region of semiconductor material is between the first region of semiconductor material and the third region of semiconductor material.
 9. The transistor of claim 8, wherein the third region of semiconductor material has a third width, greater than the first width, extending in the first direction.
 10. The transistor of claim 8, further comprising: a fourth region of semiconductor material having the first conductivity type in contact with the third region of semiconductor material, wherein the third region of semiconductor material is between the second region of semiconductor material and the fourth region of semiconductor material; wherein the third region of semiconductor material has a third width, less than or equal to the second width, extending in the first direction; and wherein the fourth region of semiconductor material has a fourth width, greater than the first width, extending in the first direction.
 11. The transistor of claim 1, wherein the second width is less than the first width, and wherein the third width is less than the second width.
 12. The transistor of claim 1, wherein the second width is equal to the first width, and wherein the third width is less than the first width.
 13. A memory, comprising: an array of memory cells comprising a first plurality of strings of series-connected memory cells and a second plurality of strings of series-connected memory cells; a first local access line connected to a control gate of a respective memory cell of each string of series-connected memory cells of the first plurality of strings of series-connected memory cells; a second local access line connected to a control gate of a respective memory cell of each string of series-connected memory cells of the second plurality of strings of series-connected memory cells; a first transistor; a second transistor; and a global access line selectively connected to the first local access line through the first transistor, and selectively connected to the second local access line through the second transistor; wherein the first transistor comprises: a first control gate isolated from a first region of semiconductor material having a first conductivity type; a first source/drain region having a second conductivity type different than the first conductivity type and formed in the first region of semiconductor material; a second source/drain region having the second conductivity type and formed in the first region of semiconductor material; and a second region of semiconductor material having the first conductivity type in contact with the first region of semiconductor material, wherein the first region of semiconductor material is between the first control gate and the second region of semiconductor material; wherein the first region of semiconductor material has a first width extending in a first direction from the first source/drain region to the second source/drain region; and wherein the second region of semiconductor material has a second width, less than the first width, extending in the first direction; and wherein the second transistor comprises: a second control gate isolated from a third region of semiconductor material having the first conductivity type, and isolated from the first control gate; a third source/drain region having the second conductivity type and formed in the third region of semiconductor material; a fourth source/drain region having the second conductivity type and formed in the third region of semiconductor material; and a fourth region of semiconductor material having the first conductivity type in contact with the third region of semiconductor material, wherein the third region of semiconductor material is between the second control gate and the fourth region of semiconductor material; wherein the third region of semiconductor material has the first width extending in the first direction; and wherein the fourth region of semiconductor material has the second width extending in the first direction.
 14. The memory of claim 13, wherein the first region of semiconductor material, the second region of semiconductor material, the third region of semiconductor material, and the fourth region of semiconductor material each have a same level of conductivity.
 15. The memory of claim 14, wherein the level of conductivity is sufficient to provide a breakdown voltage of the first transistor greater than 30V and to provide a breakdown voltage of the second transistor greater than 30V.
 16. A memory, comprising: an array of memory cells comprising a first plurality of strings of series-connected memory cells and a second plurality of strings of series-connected memory cells; a first plurality of local access lines, each local access line of the first plurality of local access lines connected to a control gate of a respective memory cell of each string of series-connected memory cells of the first plurality of strings of series-connected memory cells; a second plurality of local access lines, each local access line of the second plurality of local access lines connected to a control gate of a respective memory cell of each string of series-connected memory cells of the second plurality of strings of series-connected memory cells; a first plurality of block select transistors; a second plurality of block elect transistors; and a plurality of global access lines, each global access line selectively connected to a respective local access line of the first plurality of local access lines through a respective block select transistor of the first plurality of block select transistors, and selectively connected to a respective local access line of the second plurality of local access lines through a respective block select transistor of the second plurality of block select transistors; wherein a particular block select transistor of the first plurality of block select transistors comprises: a control gate isolated from a first region of semiconductor material having a first conductivity type; a first source/drain region having a second conductivity type different than the first conductivity type and formed in the first region of semiconductor material; a second source/drain region having the second conductivity type and formed in the first region of semiconductor material; and a second region of semiconductor material having the first conductivity type in contact with the first region of semiconductor material, wherein the first region of semiconductor material is between the control gate and the second region of semiconductor material; wherein the first region of semiconductor material has a first width extending in a first direction from the first source/drain region to the second source/drain region; and wherein the second region of semiconductor material has a second width, less than or equal to the first width, extending in the first direction.
 17. The memory of claim 16, further comprising: a third region of semiconductor material having the first conductivity type in contact with the second region of semiconductor material, wherein the second region of semiconductor material is between the first region of semiconductor material and the third region of semiconductor material; and a fourth region of semiconductor material having the first conductivity type in contact with the third region of semiconductor material, wherein the third region of semiconductor material is between the second region of semiconductor material and the fourth region of semiconductor material; wherein the third region of semiconductor material has a third width, less than or equal to the second width, extending in the first direction; and wherein the fourth region of semiconductor material has a fourth width, greater than the first width, extending in the first direction.
 18. The memory of claim 16, wherein the control gate of the particular block select transistor is a first control gate, and wherein a different block select transistor of the first plurality of block select transistors comprises: a second control gate isolated from a third region of semiconductor material having the first conductivity type, and connected to the first control gate; a third source/drain region having the second conductivity type and formed in the third region of semiconductor material; a fourth source/drain region having the second conductivity type and formed in the third region of semiconductor material; and a fourth region of semiconductor material having the first conductivity type in contact with the third region of semiconductor material, wherein the third region of semiconductor material is between the second control gate and the fourth region of semiconductor material; wherein the third region of semiconductor material has the first width extending in the first direction; and wherein the fourth region of semiconductor material has the second width extending in the first direction.
 19. The memory of claim 16, wherein the control gate of the particular block select transistor is a first control gate, and wherein a different block select transistor of the second plurality of block select transistors comprises: a second control gate isolated from a third region of semiconductor material having the first conductivity type, and isolated from the first control gate; a third source/drain region having the second conductivity type and formed in the third region of semiconductor material; a fourth source/drain region having the second conductivity type and formed in the third region of semiconductor material; and a fourth region of semiconductor material having the first conductivity type in contact with the third region of semiconductor material, wherein the third region of semiconductor material is between the second control gate and the fourth region of semiconductor material; wherein the third region of semiconductor material has the first width extending in the first direction; and wherein the fourth region of semiconductor material has the second width extending in the first direction.
 20. The memory of claim 16, wherein each block select transistor of the first plurality of block select transistors and of the second plurality of block select transistors comprises: a respective control gate isolated from a respective first region of semiconductor material having the first conductivity type; a respective first source/drain region having the second conductivity type and formed in its respective first region of semiconductor material; a respective second source/drain region having the second conductivity type and formed in its respective first region of semiconductor material; and a respective second region of semiconductor material having the first conductivity type in contact with its respective first region of semiconductor material, wherein its respective first region of semiconductor material is between its respective control gate and its respective second region of semiconductor material; wherein its respective first region of semiconductor material has the first width extending in the first direction; and wherein its respective second region of semiconductor material has the second width extending in the first direction. 